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Materials Science and Engineering R 83 (2014) 1–59 Contents lists available at ScienceDirect Materials Science and Engineering R journal homepage: www.elsevier.com/locate/mser Recent progress in resistive random access memories: Materials, switching mechanisms, and performance F Pan *, S Gao, C Chen, C Song, F Zeng A R T I C L E I N F O c om Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Tsinghua University, Beijing 100084, PR China A B S T R A C T This review article attempts to provide a comprehensive review of the recent progress in the so-called resistive random access memories (RRAMs) First, a brief introduction is presented to describe the construction and development of RRAMs, their potential for broad applications in the fields of nonvolatile memory, unconventional computing and logic devices, and the focus of research concerning RRAMs over the past decade Second, both inorganic and organic materials used in RRAMs are summarized, and their respective advantages and shortcomings are discussed Third, the important switching mechanisms are discussed in depth and are classified into ion migration, charge trapping/detrapping, thermochemical reaction, exclusive mechanisms in inorganics, and exclusive mechanisms in organics Fourth, attention is given to the application of RRAMs for data storage, including their current performance, methods for performance enhancement, sneak-path issue and possible solutions, and demonstrations of 2-D and 3-D crossbar arrays Fifth, prospective applications of RRAMs in unconventional computing, as well as logic devices and multi-functionalization of RRAMs, are comprehensively summarized and thoroughly discussed The present review article ends with a short discussion concerning the challenges and future prospects of the RRAMs ß 2014 Elsevier B.V All rights reserved ng Article history: Available online 10 July 2014 Introduction Materials Storage media 2.1 Inorganic storage media 2.1.1 Organic storage media 2.1.2 Electrode materials 2.2 Switching mechanisms Ion migration 3.1 Cation migration 3.1.1 Anion migration 3.1.2 Charge trapping/de-trapping 3.2 Interfacial charge traps 3.2.1 Charge traps provided by a middle nanoparticle layer 3.2.2 Randomly distributed charge traps 3.2.3 Thermochemical reaction 3.3 Thermochemical reaction in semiconducting metal oxides 3.3.1 Thermochemical reaction in organics 3.3.2 Exclusive mechanisms in inorganics 3.4 Insulator-to-metal transition in Mott insulators 3.4.1 The sp2/sp3 conversion in amorphous carbon 3.4.2 cu u du o Contents ng th an co Keywords: Resistive switching Resistive random access memory Nonvolatile memory Memristor Organic resistive memory * Corresponding author Tel.: +86 10 62772907; fax: +86 10 62771160 E-mail address: panf@mail.tsinghua.edu.cn (F Pan) http://dx.doi.org/10.1016/j.mser.2014.06.002 0927-796X/ß 2014 Elsevier B.V All rights reserved CuuDuongThanCong.com https://fb.com/tailieudientucntt 3 5 6 13 17 17 17 18 20 20 20 21 21 22 F Pan et al / Materials Science and Engineering R 83 (2014) 1–59 22 22 23 24 24 25 25 27 29 31 33 37 38 39 41 41 43 44 44 47 47 48 48 50 50 51 51 52 54 54 an co Exclusive mechanisms in organics Charge transfer 3.5.1 Conformational change 3.5.2 RRAMs for data storage Current performance 4.1 Methods for performance enhancement 4.2 Doping 4.2.1 Electrode engineering 4.2.2 4.2.3 Interface engineering Optimization of device structure and measurement circuit 4.2.4 Multilevel storage and conductance quantization 4.2.5 4.3 Sneak-path issue and possible solutions Diode 4.3.1 Bidirectional selector 4.3.2 Self-rectification 4.3.3 4.3.4 Complementary resistive switch Demonstrations of 2-D and 3-D crossbar arrays 4.4 Prospective applications and multi-functionalization of RRAMs RRAMs for unconventional computing 5.1 5.2 RRAMs for logic application Reconfigurable switches in FPGAs 5.2.1 Logic gates 5.2.2 Material implication logic 5.2.3 5.3 Multi-functionalization of RRAMs Involvement of spins in RRAMs 5.3.1 Interactions between photons and electrons in RRAMs 5.3.2 A combination of resistive switching and superconducting behavior 5.3.3 Challenges and prospects Acknowledgements References ng 3.5 .c om Introduction cu u du o ng th Silicon-based Flash memories, consisting of a metal-oxidesemiconductor field-effect-transistor with an additional floating gate in each memory cell, represent the state-of-the-art nonvolatile memory and represent the lion’s share of the current secondary memory market due to their high density and low cost However, Flash memories suffer from several obvious disadvantages such as low operation speed (write/erase time: ms/0.1 ms), poor endurance (106 write/erase cycles) and high write voltage (>10 V) [1] Moreover, Flash memories will reach their miniaturization limit in the near future, not for technical reasons, but for physical limitations such as large leakage currents To overcome the shortcomings of Flash memories, four emerging random access memories (RAMs) have been proposed: ferroelectric RAMs (FRAMs), magnetic RAMs (MRAMs), phase-change RAMs (PRAMs) and resistive RAMs (RRAMs) Among these memories, FRAMs and MRAMs also face the miniaturization issue because of their large memory cell size [1] For PRAMs, the large power consumption during the reversible phase transition between the amorphous and crystalline phases would be the most serious obstacle to their commercialization [1] Fortunately, RRAMs have been demonstrated to exhibit excellent miniaturization potential down to 105 >106 >107 >105 >102 >104 >102 >5 Â 103 >106 >105 >107 >102 >109 >106 >108 >10 >105 >109 >104 >105 >5 Â 105 >105 >104 – 104 >107 >5 Â 109 >4 Â 103 >105